Yesterday STO forum poster Jodocus posted a thread in which he identified a number of the starships shown in the Star Trek Online trailer.

Jodocus identified the following starships from the Federation:

Galaxy ClassThe Galaxy Class starship appeared in the trailer relatively unchanged from its appearances in the TV show. It appears to have been modified only slightly, with Jodocus observing changes in its configuration similar to those during the Dominion War.

Galaxy Class - Heavy RefitThe main difference between the heavy refit and the normal Galaxy class seems to be some reinforcement and increased impulse power, with four impulse engines.

Galaxy Class - Light RefitThe light refit of the Galaxy-class ship seems to be a scout-type ship, taking some inspiration from the New Orleans-class.

Galaxy-Shovel VariantThis ship bears a strong resemblance to the Galaxy class, but with a radical change to its saucer section. The hull now resembles a shovel. The ship looks a little bit like the Yeager-class. The ship also strongly resembles some of the starship design elements in the game Starship Creator. Jodocus speculated:

Perhaps starfleet decided the saucer-section of the Galaxy class was too large and truly posed a threat to it's crew as a major catcher of weaponsfire. This new design seems to reduce the saucer section with almost 30% of surface, making it likely easier to avoid enemy weaponsfire.

Sovereign-class refit

This Sovereign-class looks significantly different, possibly even a different class entirely, it appears to be more nimble with greater structural reinforcement. In addition, it looks as if there are some ablative armor generators. Jodocus also noted the Miranda-style rollbar between the warp nacelles.

'Donut ship' or Windrunner-class?This class looks new, not like anything we've seen in the official cannon. Judging by the prevalence in the video, this may be a fairly common ship during the time period STO is set in. This vessel seems to be based off of some of Perpetual's old artwork. Jodocus also pointed out some strong similarities to the Windrunner-class, a mod ship developed by Thulls for Bridge Commander.

Tahoe-class This is a strong combat-oriented looking vessel. It bears a strong resemblance to a ship in Perpetual's concept art, the Tahoe. This ship also looks as if it has ablative armor generators. The as of yet officially unnamed vessel is likely a serious warship.

Ambassador-Class Refit Hybrid VariationThe old Ambassador class appears to have survived its age. Two variants appeared in the trailer. It may also be an entirely new class.

One Klingon ship appeared in the trailer.

Vor'cha-class A Vor'cha-class Klingon ship appeared that looks pretty much identical to those seen in the series.

There were also Borg enemy ships that appeared in the trailer.

Borg CubeThis Borg Cube appears to be a more tactical, highly armored variant.

Borg SphereThis seems to be a fairly typical Borg Sphere, the main variation seems to be the docking port, which reflects the Borg's evolution in Voyager's Endgame episode.